This invention relates generally to gas turbine engines and more particularly to apparatus and methods for thermal management of mechanical joints in such engines.
A gas turbine engine includes a turbomachinery core with a primary gas flowpath passing serially through a high pressure compressor, a combustor, and a high pressure turbine. The core is operable in a known manner to generate a primary gas flow. In a turbojet or turbofan engine, the core exhaust gas is directed through an exhaust nozzle to generate thrust. A turboshaft engine uses a low pressure or “work” turbine downstream of the core to extract energy from the primary flow to drive a shaft or other mechanical load.
It is generally desired to seal off the primary flowpath to prevent leakage of high-pressure, high-temperature gases, so as to avoid damage to temperature-sensitive components outside the primary flowpath, for example stationary structural members, and efficiency losses, both from direct leakage and from undesirable clearance changes caused by thermal loading. One of the important seals in a gas turbine engine is the compressor discharge pressure (“CDP”) seal. Typically this will be a noncontact-type seal which includes seal teeth mounted on a rotor, surrounded by a stationary abradable member.
Thermal growth response of the CDP seal is directly related to engine performance and fuel efficiency. There is a need is to slow the natural thermal response of the stationary CDP seal member in order to match it with the relatively slow response of the rotor. A slow-responding CDP seal will rub less and maintain a tighter seal, which improves performance.
Seal response has been addressed in the past with the use of low thermal growth alloys and heat shields. However, low thermal growth alloys typically have strength limitations at high temperatures. Heat shields typically are made of sheet metal and cover the expanse of the outer diameter of the CDP seal.
Furthermore, the hardware around the CDP seal often includes a joint having a number of flanges which are bolted together. Such joints can have a short low cycle fatigue (“LCF”) life caused by large radial thermal gradients between the center and the radial edges of the flanges. The LCF life can be improved by using a single integrated flange, but such a design is not always feasible because of space limitations.